Field of Invention
The present invention relates to the technical field of environmental and chemical industry, and more particularly to a system for decreasing pressure of a supercritical water system and a method therefor.
Description of Related Arts
Supercritical water treatment technique means taking advantage of the special characteristics of supercritical water to treat organic waste and utilize resources in a high efficiency. Compared with the conventional organic waste treatment techniques, the supercritical water treatment technique has significant advantages. The supercritical water treatment technique mainly comprises supercritical water oxidation technique, supercritical water gasification technique and supercritical water hydrothermal synthesis technique. The supercritical water oxidation technique mainly aims to achieve complete oxidation of organic waste; the main object of supercritical water gasification technique aims to make organic waste gasification to produce hydrogen-rich combustible gas; and the supercritical water hydrothermal synthesis technique mainly aims to synthesize high purity nano-particles. The supercritical water oxidation technique means taking advantage of the special characteristics of the supercritical water includes low viscosity, low dielectric constant, high diffusivity and other special characteristics, so that the organic matter and oxidants completely dissolved in the supercritical water perform a rapid and thorough homogeneous reaction, wherein organic carbon in the organic matter is converted into carbon dioxide; chlorine, sulfur, phosphorus and other elements are converted into corresponding inorganic salts, the vast majority of nitrogen is converted into nitrogen, so as to achieve efficient and harmless treatment of organic waste.
The supercritical water treatment technique means taking advantages of the special characteristics of the supercritical water to achieve innocent treatment and resource utilization of organic waste, which has apparent advantages compared with the conventional organic matter treatment technique. The supercritical water treatment technique mainly comprises supercritical water oxidation technique, supercritical water gasification technique and supercritical hydrothermal synthesis technique. The supercritical water oxidation technique mainly aims at complete oxidation of organic waste degradation. The supercritical water gasification technique aims at making the organic waste generate hydrogen-rich combustible gas. The supercritical hydrothermal synthesis technique mainly aims at synthesizing high purity nano-particles. The supercritical water oxidation technique means that taking advantage of the characteristics of the supercritical water such as low viscosity, low dielectric constant and high diffusivity, in such a manner that the organic matter which is completely dissolved in the organic matter performs a rapid and thorough homogeneous reaction, and the organic carbon is converted into carbon dioxide; chlorine, sulfur, phosphorus and other elements are converted into corresponding inorganic salt, wherein the vast majority of nitrogen is converted into nitrogen, so as to achieve efficient and harmless treatment of the organic waste.
The supercritical water treatment technique is defined as the most promising waste water treatment technique in one of the six major areas listed by the US National Key Technology: Energy and Environment. Supercritical water gasification technology means that taking advantage of the special physical and chemical characteristics of the supercritical water and under the premise of without adding or adding in a small amount of oxidants, under the homogeneous condition of the supercritical water, the organic matter performs hydrolysis, pyrolysis and other reactions to generate flammable gaseous products mainly based on hydrogen. Adding a small amount of oxidants in the vaporization process of the supercritical water aims to further improve the gasification rate of the organic waste. Supercritical hydrothermal synthesis technique means that in a high pressure reactor, the supercritical water serves as reactive medium, in such a manner that metal ions perform hydrolysis and dehydration reaction in the hydrothermal medium to nucleate and grow and finally form nano-metal oxide particles with a certain size and crystal habit. By filtering and recycling nano-metal oxide to achieve resource utilization of metal ions, so as to obtain significant economic benefits.
In all of the supercritical water technique, before entering the reactor, the materials containing water need to be pressurized above the critical point of water, and cannot be discharged out of the system after the reaction is finished. This involves decreasing the temperature and pressure of materials. After the reaction is completed, cooling the materials can be achieved by a heat exchanger. The completion of the materials requires a throttle part, which meanwhile is capable of ensuring requirements of a steady pressure of the system and regulating the pressure of the system. The conventional supercritical water system adopt a pressure regulating valve to control pressure of the system and decrease the pressure, so the pressure drop of the whole system is achieved on one point, which leads to a high material flow rate here, and also easily leads to a valve failure to affect the operation reliability of the system.
In addition, during the pressure decreasing process of the supercritical water system containing solid particles, the existence of inert inorganic salt leads to severe abrasion or clogging the internal elements of the regulating valve, so it is not advisable to achieve a complete pressure decrease in a single step. Capillary buck is achieved by the flow of fluid through the small diameter capillary generated by the resistance along the way to achieve material pressure drop, and by adjusting the fluid flow into the capillary to achieve precise control of capillary pressure. It can be seen that the fluid flow in the capillary pressure decreasing means by the on-way resistance generated by flowing through a small diameter capillary by the fluid to achieve a material pressure drop, which is capable of achieving precisely controlling front pressure of the capillary by regulating the flow of the fluid entering the capillary.
It can be seen that the compared with single-valve step-down, fluid flow distance in the capillary is long and the pressure loss rate is gentle, which is capable of effectively avoiding the wear of the high-speed main fluid to the throttle element. In addition, regulating the flow rate into the capillary fluid is capable of achieving a precise control of the system pressure, so as to ensure stable and reliable operations of the system.
The capillary pressure decreasing mode has a significant advantage over the single valve step-down, but besides decreasing the pressure, it is necessary to achieve precise control of the system pressure, which requires proper connections and control operation method among the capillary buck, the valve, the pump and other equipments. At present, the control method for decreasing pressure the capillary in the supercritical water treatment system has not been reported.